A continuing problem with windmills is the positioning of the blades to rotate and produce power under low wind velocities, while, at the same time, avoiding overspeeding and damage at high wind velocities. Conventionally, a windmill will have a means to cause the entire rotor to turn to a position where the plane of rotation of the blades is parallel to the direction of the wind when wind velocity becomes excessive. This preserves the mill and prevents damage, but the blades then no longer rotate and the windmill is prevented from performing useful work under high winds. Manual operation may be required to turn the rotor to the proper safety position.
Alternatively, mechanisms have been proposed which rely upon centrifugal force generated by the turning of the rotor of the mill to cause the blades to pivot to a feathered position under high winds. These mechanisms are generally complicated, expensive, heavy, and may not be reliable.